Green Infrastructure Techniques for Coastal Highway Resilience
FHWA encourages the use of ecosystem-based
approaches in adapting to climate change (see
FHWA and DOT policy orders). Ecosystems provide
valuable services that help to build resilience and
reduce the vulnerability of people, livelihoods, and
infrastructure to climate change impacts.
The FHWA Administrator dedicated a portion of the
agency’s annual Strategic Initiatives research
budget to a project that will provide state and local
transportation agencies with research, outreach,
and technical assistance on green infrastructure,
ecosystem-based approaches for improving coastal
highway resilience. While green infrastructure can
be used in both coastal and inland environments,
this project focuses on coastal areas.
Photo from Center for Coastal Resources Management,
Virginia Institute of Marine Science
Coastal green infrastructure includes dunes, wetlands, living shorelines, oyster reefs, beaches, and
artificial reefs. These features can protect coastal transportation infrastructure from the brunt of storm
surges and open water waves. Some can adapt to sea level rise by accreting sediment or migrating
inland.
This webpage contains:
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Information on the strategic initiatives project, Green Infrastructure Techniques for Coastal
Highway Resilience.
Current resources that can assist transportation agencies considering green infrastructure
approaches to coastal resilience.
A compilation of examples of green infrastructure projects designed to protect coastal
highways.
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Project information
The Green Infrastructure Techniques for Coastal Highway Resilience project seeks to improve the
resilience of coastal roads, bridges, and highways through implementation of green infrastructure,
ecosystem-based approaches. The project will investigate techniques that could be implemented as part
of transportation planning, maintenance and construction to preserve and/or improve natural
infrastructure function, thereby increasing the resilience of highways to the effects of storm surges and
sea level rise. The project will provide information and analysis on green infrastructure techniques,
benefits, costs, feasibility, and implementation considerations that transportation professionals need to
make decisions on infrastructure projects.
The project includes the following activities:
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Pilots. FHWA will partner with state departments of transportation, metropolitan planning
organizations, federal lands, and tribes to conduct assessments of green infrastructure solutions
to improve the resilience of coastal highways to climate change impacts. Each pilot will result in
a report that provides the information necessary for decision-makers to determine if a green
infrastructure solution would meet the needs of the transportation facility in question as well as
challenges and solutions encountered that could be instructive to other transportation agencies.
A white paper will analyze the current state of practice and knowledge, placing green
infrastructure for coastal resilience into the context of transportation agency actions.
Regional peer exchanges will engage key stakeholders in the project by soliciting input,
improving understanding of the type of information that transportation practitioners need, and
refining research questions and methodologies.
An implementation guide will provide transportation professionals with guidance on designing
and implementing green infrastructure as part of transportation project planning, design,
construction, and maintenance in the coastal environment. It will provide information and
analysis on green infrastructure techniques, climate adaptation and coastal resilience benefits
and risks, co-benefits, costs, including ongoing maintenance costs, feasibility, and
implementation considerations.
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Resources
Partnership
Systems Approach to Geomorphic Engineering (SAGE) is a community of practice of federal, state, and
local agencies, non-governmental organizations, academic institutions, engineers, and private
businesses working together to: 1) Use and promote green-gray approaches to ensure coastal
community and shoreline resilience; 2) Broaden science, engineering, policy and marketing activity both
domestically and internationally; and 3) Engage community partners in regional demonstrations.
Basics
US Army Corps of Engineers Brochure on Natural & Nature-Based Features (2 pages) explains the
USACE systems approach to coastal protection, combining natural and nature-based features, structural,
and non-structural measures.
Natural and Structural Measures for Shoreline Stabilization Brochure (6 pages) provides information on
a continuum of green to gray shoreline stabilization techniques that can help reduce coastal risks and
improve resilience.
Green Infrastructure Protective Services Animation – Watch a short animation describing the
protective benefits of green infrastructure.
Tools
Sea Level Rise Viewer – Marsh Migration – Look under the “marsh migration” tab of this tool to see
how wetlands in your area may be impacted by sea level rise. Marshes on the Move – explores what’s
involved when modeling the impacts of sea level rise on coastal wetlands in the future.
Coastal Flood Exposure Mapper – Use this tool to see where your community assets, including natural
resources, are most vulnerable to coastal flooding, and use this information to start conversations about
local risk reduction strategies.
Green Infrastructure Mapping Guide – Use this guide to develop a GIS work plan to prioritize green
infrastructure for coastal resilience.
Sea Level Change Curve Calculator – outputs tables of sea level change projections by year for your
selected location and parameters.
Reports
Use of Natural and Nature-Based Features (NNBF) for Coastal Resilience, U.S. Army Corps of Engineers,
2015.
North Atlantic Coast Comprehensive Study Report, U.S. Army Corps of Engineers, 2015.
Guidance for Considering the Use of Living Shorelines, NOAA, 2015.
Ecosystem-Service Assessment: Research needs for coastal green infrastructure, Executive Office of
the President, National Science and Technology Council, 2015.
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Links
NOAA Green Infrastructure Resources
USACE Engineering with Nature
NOAA Restoration Living Shorelines
US EPA Green Infrastructure
Virginia Institute of Marine Science (VIMS), Center for Coastal Resources Management, Living
Shorelines
Coasts, Oceans, Ports & Rivers Institute (CORPI) Living Shorelines Database
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Examples of Green Infrastructure Protection of Coastal Highways
Living Shoreline to Protect Shore Road on Long Island
As part of an FHWA research project, coastal engineers analyzed the potential of a living shoreline to
protect Shore Road in Brookhaven, New York, on the north shore of Long Island. The road has
experienced erosion and failure of the embankment and is threated by inundation due to sea level rise.
Location of Shore Road indicated with star symbol in each of the images.
Shore Road (looking west) and a portion of the existing revetment shown (a) at low tide and (b) just before high tide. (Photo
credits Bret Webb)
The researchers analyzed three options, summarized below.
Summary of adaptation options and rough order of magnitude costs.
Measure
Traditional
Protection
Description
Protect and/or
reinforce the
shoulder using
revetment and wall
Pros
Increases resiliency to
waves; postpones
flooding
Cons
Increases shoreline
armoring; eliminates
marsh shoreline habitat;
maintenance
Cost
$1.3M
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Living Shoreline
Protection
Protect the road
from wave damage
using a living
shoreline approach
Abandon the
Road
Abandon the asset
and/or allow the
pavement to fail
Increases resiliency to
waves; provides
natural habitat; may
keep pace with sea
level rise
Removes long-term
burden to asset
owner; eliminates
vulnerability
Regulatory hurdles;
does not address
flooding of roadway
$0.5M
Dislocation or
$5M
condemnation of private
property; reduced
public access to
waterfront
A diagram of a possible form of a living shoreline marsh for Shore Road is shown below. The living
shoreline is a constructed marsh that parallels the 0.25-mile of roadway, with large boulders placed
along the toe (seaward edge) of the marsh to retain the fill and reduce wave energy. The rocks would be
placed in segmented groups to allow wave diffraction (i.e., bending of wave crests and scattering of
wave energy) to create a stable equilibrium shoreline position in the gaps. Nearshore segmented
breakwater systems and headland pocket beach systems are related forms of coastal engineering used
for shore stabilization which can be successfully adapted to marsh creation projects. The small
“pockets” that form in the gaps are not only effective at stabilizing the shoreline position, but they also
reduce the amount of rocks needed along the toe while increasing the total length of intertidal shoreline
and marsh edge. These gaps also provide ingress and egress for mobile species (fishes and crabs) as well
as human users.
Diagram of constructed marsh living shoreline with segmented toe protection boulders for Shore Road.
Below, a profile diagram through the constructed marsh shows the addition of clean sand fill to establish
a suitable marsh slope (preferably one that matches those in the study area); the large boulders placed
at the toe of the fill; a continuous placement of suitable geotextile fabric along the landward side of the
boulder placements to prevent loss of fill at the toe; and plantings of appropriate saltmarsh (Spartina
alterniflora) and saltmeadow (Spartina patens) cordgrass below and above high tide, respectively.
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Diagram of constructed marsh profile showing Shore Road (left), clean sand fill, toe protection boulders, and
vegetation plantings below and above high tide (MHHW) (not to scale).
With exception of the geotextile fabric, all materials could be sourced locally and should match the
native conditions and characteristics as closely as possible. For example, the size and gradation of fill
material should match that of the native material as closely as possible and vegetative plantings could
be transplanted from nearby donor marshes.
In this concept, the existing revetment has been buried by the fill to provide some redundancy for
protection of the roadway. Note that a typical profile in one of the marsh gaps/pockets would have a
modestly steeper slope and no boulder or geotextile at the toe. The shoreline slopes in these pockets
will equilibrate over time to the reduced wave energy in the gaps and consist of a mixture of sandy
beach and marsh plants. The result will be a series of pocket beaches backed by dense saltmarsh.
The living shoreline adaptation can also eliminate the repetitive wave damage that the asset
experiences at high tide. The existing saltmarshes along the roadway are already doing this now: in
those areas, there is little to no wave damage present and there is no revetment either. Laboratory
investigations show that Spartina alterniflora marshes are effective at reducing wave heights by as much
as 90% over a distance of 30 ft (i.e., through the marsh). 1 Existing marshes in the study area extend 70 ft
to 100 ft from the edge of pavement out into the harbor, and the constructed marsh described here
would be of similar size. The elevation of the new marsh will essentially protect the shoulder from
waves. Therefore, the constructed marsh should be very effective at reducing wave damage along the
shoulder. The living shoreline itself does nothing to eliminate the potential for flooding when water
levels are above the roadway elevation.
1
USACE (2013) Laboratory Studies of Wave Attenuation through Artificial and Real Vegetation, U.S. Army Corps of
Engineers, ERDC TR-13-11, Washington, DC, 93 pp.
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Considering future sea level rise, some studies suggest that saltmarshes are at least keeping pace with
the present-day rate of sea level rise in the Long Island Sound area. 2 This suggests that the living
shoreline adaptation may function as well in the future as it does at the time of construction with
regards to wave height attenuation and protection of the roadway shoulder.
In terms of constructability, the techniques for construction will be less common but should be easily
accomplished by a coastal marine contractor with restoration experience. The material costs could be
considerably less than the traditional “hard” protection. There may be a need for some adaptive
management including providing supplemental plantings through the first several growing seasons
depending on the success of the planted marsh and related to sand movement in response to the
establishment of a new equilibrium with the structures.
Obtaining the required coastal construction permits will be more involved for the living shoreline
adaptation as compared to a traditional armoring adaptation. This is because the living shoreline option
involves activities seaward of mean high tide and filling of water bottoms. One way to address this may
be with a special variance as a living shoreline demonstration project. Similar projects have been
allowed as demonstration projects with some level of required monitoring around the country. The
regulatory framework in some states (e.g., Alabama, Maryland, Mississippi, New Jersey, North Carolina)
has been modified to facilitate such projects, where they are suitable alternatives to traditional
shoreline armoring, under general coastal construction permits.
Source: FHWA research
Living Levee and Breakwater to Protect San Francisco Bay Bridge Touchdown
As part of an FHWA-funded pilot, the Metropolitan Transportation Commission (MTC), the MPO for the
San Francisco Bay Area, conducted a detailed analysis of installing a living levee in combination with a
breakwater to protect the Bay Bridge touchdown from sea level rise, storm surge, and waves.
Without protection, the site would be inundated under the following scenarios:
36 inches of sea level rise (permanent inundation)
24 inches of sea level rise coupled with a 1-year tide event
18 inches of sea level rise coupled with a 2-year tide event
12 inches of sea level rise coupled with a 5-year tide event
Existing conditions coupled with a 50-year tide event.
A living levee would protect against future inundation and flooding due to sea level rise and storm
surges. A breakwater would reduce wave heights and protect the areas from future wave overtopping
and wave-induced erosion. The pilot developed a conceptual design that would protect the bridge
touchdown and toll plaza area against at least a mid-century sea level rise (approximately 12 inches)
2
Cochran, J.K., Hirschberg, J.W., and Dere, C. (1998) Atmospheric Deposition of Metals to Coastal Waters (Long
Island Sound, New York U.S.A.): Evidence from Saltmarsh Deposits. Estuarine, Coastal and Shelf Science 46, 503522.
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coupled with a 100-year extreme tide event. The design includes freeboard to meet the requirements
for FEMA accreditation, protect against wave overtopping, and be adaptable to accommodate higher
sea level rise magnitudes (36 inches). The proposed placement of the living levee and breakwater are
shown below.
Living Levee
Breakwater
A living levee has a flatter seaward slope than a traditional levee in order to allow for the planting of
vegetation, the creation of marsh habitat, the dissipation of wave energy, and the space to
accommodate future adaptive management efforts that may be needed as sea levels continue to rise.
The drawing below shows a cross-section of the living levee conceptual design.
The breakwater was designed for a wave height with an approximate 25-year return period. The larger
northeastern segment of the breakwater is oriented perpendicular to the design wave direction and the
shorter southwestern segment is oriented to minimize impacts to longshore sediment transport. The
drawing below shows a cross-section of the breakwater conceptual design.
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Implementing the living levee and breakwater would involve large scale construction in the bay, which
triggers complex environmental and regulatory requirements. This requires the collaboration of
multiple agencies, including Caltrans, the Port of Oakland, Alameda County, East Bay Regional Parks
District, San Francisco Bay Conservation and Development Commission, Regional Water Quality Board,
Bay Area Toll Authority, California Department of Fish and Game, California State Lands Commission,
California State Parks, NOAA, and USACE.
The analysis indicates that the strategies would save $15 million in daily avoided mobility costs to the
region (hours of delay, vehicle miles traveled, air pollutants) and protect 40 acres of wetlands. The
conceptual level cost estimate is $5.4 million for the living levee and $11.6 million for the breakwater,
which includes a 40% contingency.
See the full chapter for detailed analysis of the climate change impacts to the site, the conceptual
design, regulatory considerations, benefits, costs, operations and maintenance.
Source: Chapter 5 (24 pages) of MTC, Climate Change and Extreme Weather Adaptation Options for
Transportation Assets in the Bay Area Pilot Project, December 2014. http://mtc.ca.gov/tools-andresources/digital-library/climate-change-and-extreme-weather-adaptation-options
Living Shorelines Projects in Maryland
that Protect Coastal Roads
The Maryland Department of Natural
Resources (DNR) has an active living
shorelines program that works with
private landowners and public agencies
to install ecosystem-based shoreline
protection that offers better protection
than traditional hard structures without
negatively impacting adjacent
properties. DNR provides loans and
grants to finance the projects. Loan
repayments are used to fund new
projects. Maryland’s 2008 Living
Shorelines Law and 2013 regulations
serve as a model for other states.
Several of the projects have been
Image of a living shorelines project protecting MD -5 at St. Mary’s College
of Maryland from flooding of a tributary of the Chesapeake Bay.
partnerships with local agencies to
protect roads (see table below). In
addition, DNR is currently partnering with the Maryland State Highway Administration on a living
shorelines project to protect Hambrooks Boulevard in Cambridge, MD.
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Living Shorelines Projects in Maryland that Protect Roads
PROJECT NAME
COUNTY
ROADWAY
LOCATION
LIVING
SHORELINE
PROJECT TYPE
LENGTH
(L.F.)
PROJECT
COST
DATE
COMPLETE
Bay Ridge SECD
Anne Arundel
Bay Drive
Breakwaters
2,250
$1,039,910
1/1992
Town of Vienna
Dorchester
Water Street
Stone Sill
305
$157,472
12/2001
Our Lady Star of
the Sea
Calvert
Solomon's Is.
Road
Stone Groins
430
$144,987
12/2004
Penttinen, E.W.
& E.R.
Columbia Beach
SECD
Arey, P.H.
Anne Arundel
Deep Creek
Avenue
Crowner
Road
Wiltshire
Lane
Stone Sill
100
$22,724
6/2011
Stone Sill
2,346
$485,000
10/2011
Stone Sill
172
$62,188
5/2012
Gibson Road
St. Mary's
Gibson Road
Stone Sill
260
$94,973
7/2013
Lord R.L. &
Zearfoss N.
Annapolis Cove
SECD
Town of
Charlestown LS
project
Dorchester
County (tire
recycling center)
LS project
Mid-Hoopers
Island Rd
St. Mary's
Gibson Road
Stone Sill
330
$108,015
6/2014
Anne Arundel
Comm.
Access Road
BaltimoreColonial &
Tasker Lane
Hoopers
Island Road
Stone Sill/Groins
720
$209,425
10/2013
Revetment/Groins
677
$319,900.00
12/2006
Stone Sill
627
$102,197.00
12/2002
Dorchester
Hoopers
Island Road
Breakwaters
1200
$552,963.00
6/1996
McCready's Point
Rd
Dorchester
McCready's
Point Rd
Breakwaters
330
$411,485.00
6/1995
9,747
$3,711,239.00
TOTALS:
Anne Arundel
Anne Arundel
Cecil
Dorchester
The living shoreline strategy requires understanding coastal processes and working with them rather
than against them. The projects are very site specific because of differing bathymetry and exposure.
However, the projects in Maryland typically have a structural component to break the waves,
approximately 30 foot wide sand deposition, and native vegetation. Maryland has also been able to
standardize some of the criteria for deciding among types of projects (see table below), materials (sand,
rock, etc), construction practices (such as ensuring three points of contact between stones) and a
general construction specifications package.
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Maryland’s Criteria for Determining Living Shoreline Project Type
Water depth (ft)
Fetch (miles)
Erosion (ft/yr)
Wave energy
Type
Cost per linear
foot
Creek or Cove
1
0.5
2 or less
low
Non-structural:
Beach
replenishment
Fringe marsh
creation
Marshy islands
Coir logs edging
and groins
$100 - $200
Minor River
Major Tributary
1 to 2
2 to 4
1 to 1.5
2 or more
2 to 4
4 to 8
medium
medium
Hybrid:
Marsh fringe with stone groins
Marsh fringe with stone sills
Marsh fringe with stone
breakwaters
Marsh edging with stone
Stabilization of streambanks with
vegetation and stone
Stone breakwaters with beach
replenishment and appropriate
vegetation
$350-$400
$450-$600
Chesapeake Bay
4 to 15
2 or more
8 to 20
High
Structural:
Bulkheads
Revetments
Stone reinforcing
Pre-case concrete
units
$500-$1,500
Source: MD DNR
After many years of conducting living shorelines projects, Maryland DNR has developed a process that
allows the regulatory and permitting process to go smoothly and for projects to be implemented in a
timely fashion. DNR organizes a pre-application meeting with all of the regulatory agencies, which
include USACE, Fisheries, Maryland Historical Trust, and the Maryland Department of Environment, as
well as the local public. This allows the interested parties to provide feedback that will save time and
energy later on, after the formal application has been submitted. DNR has standard specifications and
bid documents for design engineers for the projects as well as a list of vetted contractors. After a
contractor is selected, the design process usually takes about one month. Then the permitting and
approvals process takes about six to eight months. After permitting, the project is put out to bid and
construction typically requires one to two months. Ongoing maintenance is important to project
success.
An assessment study of 200 living shorelines sites in Maryland found that these projects successfully
maintain coastal processes and reverse erosion. Prior to installation of the living shoreline projects, the
sites are typically experiencing about 2 feet per year of erosion. Hurricane Isabel in 2003 brought an 8
foot storm surge to Maryland shores and provided a test to the living shorelines projects. The projects
functioned as designed, attenuating wave forces, protecting the structure behind them, and maintaining
sand and soils in place due to the vegetation root structure. Following Isabel, DNR experienced a surge
in demand for living shorelines projects from landowners who observed that their neighbor’s properties
with living shorelines projects were well protected from Isabel.
Source: Interview and emails with Bhaskar Subramanian, Maryland Department of Natural Resources.
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Plumb Beach Re-nourishment Project
This project, managed by the US Army Corps of Engineers, is to reduce coastal storm risk to Plumb Beach
and the Belt Parkway in Brooklyn, NY.
Phase I was completed in late 2012 and involved placing approximately 127,000 cubic yards of sand in
the severely eroded Plumb Beach area along the Belt Parkway, a busy highway and a critical piece of the
city’s infrastructure. The sand was placed just prior to Hurricane Sandy’s arrival and helped prevent
serious damage to the Belt Parkway. Phase I also involved the installation of a temporary geotube groin
structure to help mitigate the loss of Phase I sand while the Corps awaited the ability to award Phase II.
Phase II involves the construction of two permanent stone groins at each end of the beach to help
mitigate erosion in the long run. It also involves the construction of a permanent stone breakwater in
the water off of the severely eroded area essentially parallel to the beach to mitigate future sand loss.
Phase II also involves planting vegetation in sand dunes to help strengthen them as well as the
installation of sand fencing to trap sand blowing landward.
While Phase I provides immediate coastal storm risk reduction benefits to both the Belt Parkway and the
frequently used bike path along it, Phase II is designed to keep the coastal storm risk reduction benefits
in place longer by managing the movement of sand and greatly reducing the need for future renourishments at the project site.
The local cost-sharing sponsor for both phases of the project is the New York City Department of Parks
and Recreation with 65 percent of funding being federal and 35 percent being local. Phase I was
completed through a $3.5 million contract with Great Lakes Dredge and Dock based out of Oak Brook,
Ill., and beneficially reused sand dredged from Ambrose Channel as part of ongoing efforts to deepen
the navigation channels associated with the Port of New York and New Jersey. A $2 million contract for
Phase II was awarded to Village Dock, Inc., of Port Jefferson, NY.
Source: Excerpted and modified from USACE Press Release, February 6, 2013
Beach Nourishment to Protect Sections of California Highway 1
The Association of Monterey Bay Area Governments developed a plan identifying four strategies to
reduce coastal erosion along southern Monterey Bay in California. One of these strategies involves
beach nourishment to protect critical infrastructure, including sections of California Highway 1.
Source: Association of Monterey Bay Area Governments, Coastal Regional Sediment Management Plan
for Southern Monterey Bay, 2008
Protections for Louisiana Highways LA-27, LA-82, and LA-182 in the Louisiana Coastal Master Plan
In 2012, Louisiana’s Coastal Protection and Restoration Authority developed a Coastal Master Plan to
provide a system-wide plan for reducing hurricane flood risk and restoring land along the Louisiana
coast. The Plan defines a set of coastal protection and restoration projects to be implemented by the
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state over the next 50 years. Six of these projects create wetlands in order to protect sections of
Louisiana’s highways. The criteria used for selecting projects consider future climate impacts.
Several Louisiana highways are vulnerable to flooding from hurricanes, including LA-27, LA-82, and LA182. To shield these highways, the Plan selected six land restoration projects that will create protective
wetland buffers. One type of project involves hydrologic restoration, which repairs degraded wetlands
by removing blockages to the natural flow of water. Restoration is accomplished by conveying water to
areas that had been previously cut off by man-made levees or other built structures. In the Mermentau
Basin, three projects will increase the flow of freshwater to wetlands adjacent to LA-27 near Creole and
sections of LA-82 near Grand Chenier and Pecan Island. An additional project will increase connectivity
among wetlands on either side of LA-182 in the Chacahoula Basin. Connected wetlands will become
more robust and provide a stronger natural barrier against shoreline erosion.
To provide additional protection for LA-82, the Plan also selected a marsh creation project to establish
new wetland habitat near Grand Chenier, and a shoreline protection project to construct rock
breakwaters along the Schooner Bayou Canal near North Prong. Breakwaters are walls that extend out
into a body of water to protect a shoreline from the impact of waves. These breakwaters are intended
to dampen wave energy and prevent degradation of existing wetlands adjacent to the highway.
Source: State of Louisiana, Coastal Protection and Restoration Authority, Louisiana’s Comprehensive
Master Plan for a Sustainable Coast, 2012.
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